1. Field of the Invention
The present invention relates to a brazing material in the form of a composite foil which is used for joining ceramics to each other or to metal. The composite foil is made up of a core of Ti and outer layers of Ni or an Ni alloy containing a specific amount of Cu. This brazing material is suitable for joining oxide ceramics to each other or to a highly wettable metal having a coefficient of thermal expansion close to that of ceramics, or to a Kovar alloy or a Cu composite material. It provides good workability and high bond strength.
2. Description of the Prior Art
According to the conventional technology for ceramics packaging, the joining of ceramics to each other is accomplished by the steps of metallizing the surfaces facing each other with a metal such as Mo, W, and Mo-Mn, which is highly wettable and has a coefficient of thermal expansion close to that of ceramics, plating the metallized surface with Ni, and Ag soldering. This joining method, however, needs much time and high cost in metallizing, Ni plating, and Ag soldering, and presents difficulties in joining ceramics plates having irregularly shaped surfaces.
The joining of ceramics to metal is also accomplished in the same method as mentioned above. In addition to this method, a variety of joining methods have been developed so far. They include, for example, the high-melting metal method and the active metal method. Unfortunately, they need complex steps and strict environment controls and hence lead to high production cost.
Prior arts relating to this technology are disclosed in U.K. Patent No. 761045 and Japanese Patent Laid-Open No. 37914/1977. According to the former disclosure, Cu is placed on a substrate and heated to a temperature higher than the melting point of Cu and lower than the melting point of cuprous oxide so that Cu oxide is formed on Cu. Joining is accomplished by the reaction of the substrate with a eutectic of Cu oxide and molten Cu. According to the latter disclosure, joining is accomplished by forming between ceramics and metal a eutectic alloy whose major component is the metal to be joined to ceramics. To be more specific, the joining of Fe to ceramics is accomplished by heating to as high as 1523.degree. C. which is the eutectic point of Fe and oxygen. In this case, oxygen functions as a binder. Moreover, the joining of Cu to ceramics is accomplished by heating to a temperature higher than the eutectic point (1065.degree. C.) of Cu and oxygen and lower than the melting point (1083.degree. C.) of Cu.
These joining methods have some disadvantages. That is, the range of heating temperature is narrow, heating up to a high temperature (1523.degree. C.) is necessary for the joining of Fe to ceramics, and the joining operation needs many steps and hence costs much.